The present invention relates to a dustproof linear actuator adequate for use inside a clean room.
An example of the conventional dustproof linear actuator is disclosed in Unexamined Japanese Utility Model Publication No. Hei. 7-7837. The linear actuator includes a linear guide device disposed within a housing shaped in a long box, a carriage guided by the linear guide device, and a linear drive device for driving the carriage in the axial direction by a ball screw device. A slit which extends in the moving direction of the carriage is formed in the upper surface of the housing. The head portion of the carriage passes through the slit to protrude from the housing to an external. A neck portion of the carriage, located in the slit, connects the carriage to its head portion. The carriage transports an object to be transported in a state that the object is mounted on the head portion thereof.
Where the slit is left open, dust particles freely enter the housing and exit therefrom through the slit. To prevent the free movement of the dust particles, the linear actuator includes pulleys which are disposed close to both ends of the housing and a looped sealing band which is firmly attached to the fore and the read sides of the carriage. The looped sealing band is circulatively turned along the pulleys in accordance with the linear movement of the carriage. The sealing band tightly closes an opening defining the slit.
Where the linear actuator of the dust-proof type is used as a transporting device inside a clean room, it needs to prevent the dust particles within the linear actuator from leaking toward the external so that the clean room is polluted. It has been desired that the linear actuator should be further improved for the dust proof.
The present invention has been accomplished under conventional circumstances and has an object of providing a dustproof linear actuator which remarkably prevents the dust particles from leaking out of the housing by reducing the pressure inside the actuator.
To achieve the above object, there is provided a dustproof linear actuator having: a housing with a slit extending axially; a linear guide device disposed in the housing; a carriage mounted in the housing and axially movable along the slit by the linear guide device, the carriage including a workpiece mounting table protruding from the housing through the slit; a linear drive device disposed in the housing for moving the carriage axially; a pair of pulleys disposed in an axial end of the housing; and a sealing band mounted around the pulleys within the housing movably for closing the slit, the sealing band including first and second ends which are fastened to first and second ends of the carriage, respectively, to form a circulative loop. Further, the dustproof linear actuator has an air venting device for venting air existing in the housing close to the axial end toward an outside of the housing so that the dustproof linear actuator can remarkably prevents the dust particles from leaking out of the housing by reducing the pressure inside the actuator.
By sucking air from a space enclosed by the sealing band and the housing in the linear actuator, the inside of the linear actuator is kept at a negative pressure, to thereby prevent the dust particles from being scattered outside. Particularly, when the carriage is moved to the end of the housing, air in the housing is compressed by the moving carriage so that the pressure is increased. Under this condition, the dust particles tend to release outside the actuator. However, the present invention successfully solves the problem of the pressure increase by locating the openings for sucking air from the actuator near to both ends of the housing.